API Gateway Proxy Headers as http.Header

[jackwellsxyz]

Hello! Any chance we could make the events.APIGatewayProxyRequest.Headers type to match http.Header? It would be nice to take advantage of the http.Header helper functions. Basically have to convert map[string]string to map[string][]string.

[bmoffatt]

To maintain backwards compatibility. I don't think that events.APIGatewayProxyRequest.Headers's type can be changed

This might instead be achieved by adding a func (r *APIGatewayProxyRequest) Header() http.Header {}

[piotrkubisa]

I also don't think events.APIGatewayProxyRequest.Headers should be given in http.Header format. Of course here goes compatibility reasons and having concise API, but also transformation from map[string]string to http.Header (exactly: map[string][]string) on first glance look simple but then you notice there is a lot computation involved, and not usually it is needed for everyone.

If you are transforming a event into a http.Request you may like https://github.com/apex/gateway or http://github.com/piotrkubisa/apigo. Also if you need only http.Header map you definitely find something interesting in tj's code or in my fork and adapt it to your use case. Please note: transformations between events.APIGatewayProxyRequest to http.Request are not cheap (btw. most of time is spent on headers transformation).

[piotrkubisa]

One note related to my previous comment: If #136 will be merged then it will easy to cast into http.Header:

headers := http.Header(event.MultiValueHeaders)

Please note: type-casting map to http.Header won't change keys of headers to follow format of the
canonical MIME headers (e.g. Accept-Encoding, Content-Type, User-Agent). Example below might illustrate a problem:

m := map[string][]string{
	"foo-Bar": {"World"},
}

h := http.Header(m)
fmt.Println(h.Get("Foo-Bar"))
// Output: "" (empty string)

Personally, I'd stick to folllowing:

headers := make(http.Header)
for key, values := range event.MultiValueHeaders {
    for _, value := range values {
        headers.Add(key, value)
    }
}

@bmoffatt Could you tell me if it is superfluous to check multiValueHeaders (also multiValueQueryStringParameters) are populated (i.e. via len(event.MultiValueHeaders) > 0) and fallback to event.Headers when they aren't? Is it safe to only use multiValueHeaders instead of headers (the same question applies to multi-value query strings instead of single-value query strings)?